Laser cutting system

ABSTRACT

A laser cutting system has a specially designed frame that allows the laser cutting head to be mounted to the underside of a cross beam for a more efficient movement. The frame is further designed so as to allow the accessing of the work area of the laser cutting system along three different directions. The movement of the laser cutting head for fabricating a sheet placed in the work area of the laser cutting system is effected by a process that takes into consideration a number of parameters and determined data all of which are interpolated for generating optimal movements to further enhance the operating efficiency of the laser cutting system. The laser resonator of the laser cutting system of the instant invention is configured to have a telescopic system that maintains the density and power of the laser beam by auto focusing the same so that optimum cuts can be effected irrespective of whichever area of the worksheet is to be fabricated. A special design worktable in the working area of the laser cutting system provides support for the worksheet.

FIELD OF THE INVENTION

The present invention relates to a laser cutting system that has newdesigns at least with respect to its frame, its laser output mechanism,the process of outputting the laser for fabricating a worksheet, and theworktable system to which the worksheet is placed.

BACKGROUND OF THE INVENTION

Flying optic laser cutting systems are known. However, the prior artsystems tend to have a number of shortcomings that limit their speed andefficiency. Some of these shortcomings result from, for example, thedesign of the frame that supports the cutting head of the laser cuttingsystem, the design of the cutting mechanism itself, the way in which thecutting process is effectuated, the limited way in which a machine maybe installed and, once installed, the limited accessing of the machineby the operator.

The laser cutting system of the instant invention aims to improve onevery aspect of the aforenoted shortcomings of current laser cuttingsystems by, specifically, providing a new frame for the system, animproved laser cutting mechanism, and a more efficient process ofeffecting cutting. In addition, the laser cutting system of the instantinvention is provisioned with a worktable system that enhances thecutting of a worksheet placed thereon, as well as for evacuating anydust and/or exhaust gases resulting from the fabricating of theworksheet efficiently away from the laser cutting system.

SUMMARY OF THE INVENTION

The present invention laser cutting system is built on a frame that hasa cross beam supported by two structures. The cross beam is designed tohave a trapezoidal structure for movably supporting a laser cutting headthat hangs therefrom. The laser cutting head in turn is mounted to abase member that has arms extending in a direction perpendicular to thelongitudinal axis of the cross beam. As a consequence, the cutting headcan move along the longitudinal axis of the cross beam as well as thelongitudinal direction along the axis of the arms extending from thebase member. To effect the movement of the base member bidirectionallyalong the longitudinal axis of the cross beam, a linear drive mechanism,in the form for example of a magnet drive, may be used. A linear drivemay also be used for moving the cutting head along the direction of theextending arms of the base members. For the movement of the cutting headalong the vertical direction, a servomotor is mounted to the basemember, or more specifically the skeleton frame of the base member towhich the cutting head is mounted, so that the cutting head can be movedin a direction perpendicular to the respective longitudinal axes of thecross beam and the extending arms.

The cross beam of the frame of the laser cutting system is supported, atboth ends, by respective support structures, which may be unitarystructures. One the structures is configured to have a bore throughwhich exhaust gases and/or dust particles resulting from the fabricatingof a worksheet by the laser beam output from the cutting head may bevented away from the laser cutting system. The other of the supportstructures is configured to have an opening through which worksheets maybe conveyed to or removed from a support table, such as for example aworktable or a cassette placed underneath the cross beam. The worksheetsmay also be conveyed to/from the laser cutting system from either sideof the cross beam in a direction perpendicular to the longitudinal axisof the cross beam. To provide further rigidity for the frame of thelaser cutting system, two truss members connect the support structuresat their respective bases.

To control the movement of the laser cutting held a processor means,such as for example a computerized numerical controller (CNC), isprovided in a housing positioned relative to the frame. The CNC, inaddition to controlling the respective movements of the various drivemotors that move the cutting head along the various directions, alsocontrols the outputting of the laser beam to the cutting head by thelaser generator, which is also positioned adjacent and/or relative tothe frame.

For the laser cutting-system of the instant invention, the laser beamoutput from the laser beam generator, or resonator, is reflected by anumber of mirrors with the focal point of the laser beam for fabricatingthe particular material of the worksheet to be focused by a motormechanism internal to the cutting head. To maintain the distance relatedto the widening or focusing of the axial symmetric laser beam, the lasergenerator of the inventive laser cutting system has a telescopemechanism, positioned within the laser generator itself, that workscooperatively with the output coupler of the laser resonator formaintaining the density and the power of the laser beam to constantvalues for a predetermined distance, so that the power of the laser beamrequisite for effectively fabricating the worksheet is maintained forevery portion of the worksheet. The telescope mechanism has two mirrors.One is the output coupler from the laser resonator. The other is thelens that moves relative to the output coupler. The lens is drivenrelative to the coupler by a motor, which is controlled by software ofthe system according to some preset parameters. These parametersinclude, among other things, the distance separating the lens from thesheet material, i.e. the focusing lens distance.

Such auto-focusing of the laser beam is done automatically by acognizance of a predetermined distance that the laser beam is to beoutput, the type of material being fabricated, and the type oftelescopic mechanism to be used. Moreover, by taking into considerationthe actual length of the laser beam and by dividing the maximum useablelength of the laser beam into a number of zones, i.e., differentquadrants or sectors, the focal point of the laser beam may becorrected. The focus of the laser beam for the different areas of theworksheet may be adjusted by moving the laser cutting headbidirectionally along its vertical axis to maintain respective optimalfocal points for worksheets of different materials.

To compensate for the deficiencies inherent in the different areas ofthe worksheet which may be due to their respective locations withreference to the center of the worksheet, the worktable or cassette ontowhich the worksheet is placed has its areas divided into a number ofportions each with correction factors determined empirically, so thatsuch correction factors may be taken into account when a particularlocation of the worksheet which corresponds to the location on theworktable to which that portion of the worksheet superposes is to befabricated by the laser beam output from the cutting head. Thesecorrection factors are stored in a memory that may be part of the CNCcontroller.

With respect to the way in which the laser beam output from the lasergenerator is to be directed, a number of reflective mirrors are used. Toenhance the alignment process, unlike the prior art systems that requireextensive removal and reassembly of the various mirrors for alignment ofthe laser beam, the reflective mirrors of the instant invention lasercutting system are configured such that alignment can easily be effectedby the removal of a single one of the mirrors. Further, the reassemblyof the mirror into the system does not require any further realignmentof the laser beam. This is done by configuring the opening of the mirrorholder to have a dimension large enough to allow the removal of themirror while leaving the mirror holder fixed to the support of thedevice and allowing the laser beam to freely pass.

The laser cutting head being used with the laser cutting system of theinstant invention, but for a number of modifications, could be anycutting head that is sold by a number of manufacturers. One of theimprovements of the cutting head of the instant invention is theprovision of a servomechanism, via feedback, for automatically adjustingthe focus lens inside the cutting head so as to enable the automaticadjustment of the focus point for different types of materials that maybe fabricated by the laser beam output from the cutting head. Anotherimprovement of the cutting head of the instant invention is theprovision of a partition window somewhere within the cutting head forisolating the focusing lens from particles that may ricochet against thefocusing lens when the worksheet is being pierced or cut by the laserbeam. This is particularly true when the laser process is not stable orwhen the parameters for cutting are not set properly. Such partitionmeans may be in the form of a diamond window that has the properties ofbeing translucent so as to allow the laser beam to pass therethrough aswell as having the hardness for withstanding the impacts of thericocheting particles. Other partition windows that have the samequalities as a diamond window may also be used.

To enhance the fabrication of a worksheet, the movement of the cuttinghead and the directing of the laser beam thereto are controlled by theCNC in a process that takes into consideration the distance separating alocation on the worksheet for which work is being done to a nextlocation on the worksheet to which the next piercing by the worksheet isto be effected. To effect the optimal movement of the cutting head fromone location to the next, variables such as acceleration anddeceleration of the cutting head, the height of the cutting head withrespect to the cutting sheet, or the focal point for the material towhich the worksheet is made of, are taken into consideration. Themovement of the cutting head relative to the worksheet may be termed a“ping pong” effect in that the cutting head moves in an optimal mannerfrom point to point for piercing various holes and cuts on theworksheet.

The worktable onto which the worksheet is placed is made up of a frame,in the shape of a cassette, that is movable in directions perpendicularto the longitudinal axis of the cross beam. The movement of the cassetteis effected on a couple of rails, or guides, onto which the cassetterides. Within the cassette there are a number of strips, each having anumber of bores formed therealong extending along the length of thecassette. A number of brackets extend in a direction perpendicular tothe strips at predetermined positions along the cassette. These bracketseach have a number of equally spaced slots formed therealong. Aplurality of ribs are fitted to equally distanced slots of the bracketsso that the ribs and the strips that have the bores are alternatedthroughout the cassette along its longitudinal direction. The ribs eachare formed with a number of contiguous teeth at its top portion. Intoeach bore of each strip a pin is inserted. The plane that is formed bythe tips of the pin is higher, although not by much, than the plane thatis formed by the tip of the contiguous teeth of the ribs. Thus, it isthe tip of the pins that support the worksheet on the cassette. If theworksheet flexes, or when the worksheet is being cut, the tips of thecontiguous teeth of the ribs would provide support for those portions ofthe worksheet that fall below the plane formed by the tips of the pins.

By being able to roll along the rails, the cassette is movable between alocation under the cross beam for the fabrication of a worksheet placedthereon, and a location that is away from the frame of the laser cuttingsystem, so that the finished worksheet may be removed, and be replacedby a to be fabricated worksheet.

The cassette is placed over a suction frame structure that has a numberof sections each adaptable to provide vacuum to a corresponding portionof the cassette. Thus, by activating the particular section of thesuction base, particles resulting from the fabrication of the worksheetby the laser beam are suctioned away and vented through the bore at oneof the support structures of the frame away from the laser cuttingsystem.

It is therefore an objective of the present invention to have a framedesigned for providing a more efficient way of mounting a cutting headfor a laser cutting system.

It is another objective of the present invention to provide a lasercutting system that has an improved laser resonator having means thatcan provide auto-focusing.

It is yet another objective of the present invention to provide animproved cutting head for a laser cutting system that does not requireits focusing lens to be replaced as often as those in conventional lasercutting heads.

It is still another objective of the present invention laser cuttingsystem to provide a process of more efficiently moving the cutting head.

It is still yet another objective of the present invention to provide aworktable that enhances the fabrication of a worksheet placed thereon bya laser beam.

It is therefore an overall objective of the present invention to providea flying optic laser system that operates in a way that is moreefficient than prior art laser cutting systems.

BRIEF DESCRIPTION OF THE DRAWINGS

The above mentioned objectives and advantages of the present inventionwill become apparent and the invention itself will be best understood byreference to the following description of an embodiment of the inventiontaken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a perspective view of the frame structure of the laser cuttingsystem of the instant invention;

FIG. 2 is a second perspective view of the frame structure of the lasercutting system of the instant invention;

FIG. 3 is a perspective view of the base member that is to be mounted tothe cross beam of the FIGS. 1 and 2 frame structure;

FIG. 4 is a perspective top view of the FIG. 3 base member;

FIG. 5 is a bottom view of the frame structure of FIG. 2;

FIG. 6 is a perspective view of the frame structure of FIGS. 1 and 2having mounted thereto the base member of FIG. 3;

FIG. 7 is a perspective view of the FIG. 5 frame structure illustratingthe underside of the cross beam and the support structures of the FIGS.1 and 2 frame structure;

FIG. 8 is a cross sectional view of the FIG. 1 frame structure with thebase member of FIG. 3 shown in relationship to the cross beam;

FIG. 9 is a perspective view of the frame structure of FIG. 1 covered bythe appropriate doors and having attached thereto the cabinet housingsfor the laser resonator and the processor controlling unit;

FIG. 10 is another perspective view of the FIG. 9 frame structureshowing the opening at one of the support structures;

FIG. 11 is yet another perspective view of the laser cutting system ofFIG. 10 showing access to the work area of the system by means of theopening at one of the support structures and also at one side of thelaser cutting system;

FIG. 12 is a perspective sectional view of the cross beam and the basemember that is movably mounted to the cross beam;

FIG. 13 is another perspective view of the cross beam and the basemember, as viewed from another end of the cross beam;

FIG. 14 is a perspective view of the frame structure and the base memberand the laser resonator mounted adjacent to the frame for illustratingthe path of the laser beam from the laser resonator to the cutting headof the laser cutting system of the instant invention;

FIG. 15 is a plan view illustrating the laser resonator, the insidecomponents of the laser resonator, and the alignment of the laser beamfrom the laser resonator, as well as the path of the laser beam to thecutting head;

FIG. 16 contains a frontal view of the reflective mirror of the lasercutting system of the instant invention used for alignment of the laserbeam;

FIG. 17 is a perspective view of the reflective mirror of the lasercutting system of the instant invention;

FIG. 18 is a disassembled view of a laser cutting head;

FIG. 19 is an assembled view of a portion of the laser cutting head ofFIG. 18 illustrating in particular the placement of a partition lens forprotecting the focusing lens of the laser head;

FIG. 20 is an illustration of the focusing of the laser beam at thevarious partitioned locations of a worktable;

FIG. 21 is an illustration of the routing of a laser beam and thecooperation between the telescopic device and the output coupler in thelaser generator for regulating the focusing of the laser beam;

FIG. 22 is an illustration for enhancing the understanding of how thecutting head of the instant invention laser cutting system is moved;

FIG. 23 is a plan view of a worksheet with various holes therein forfurther illustrating the cutting head movement of the instant invention;

FIG. 24 is a flow chart illustrating the process of moving the lasercutting head of the instant invention;

FIG. 25 is a sectional perspective view of the various components thatmake up a worktable cassette;

FIG. 26 is an enlarged perspective view of a corner section of thecassette of FIG. 25;

FIG. 27 is a front view of a portion of the cassette, and how it rideson the rails as shown in FIG. 25;

FIG. 28 is a perspective view of the base of the worktable of theinstant invention laser cutting system that is adaptable to providesuction at the various portions of the cassette placed thereover;

FIG. 29 is a second perspective view of the base shown in FIG. 28;

FIG. 30 is an end view of the laser cutting system of the instantinvention with the cassette and the suction provided base all shown inrelative relationship with the frame structure of FIGS. 1 and 2; and

FIG. 31 is an illustration of the auto-focusing feature of the instantinvention system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIG. 1, a frame structure of the laser cutting systemof the instant invention is shown. This frame structure 2 has a crossbeam 4 being supported by two support structures 6 and 8. Supportstructure 8, as best shown in FIG. 2, comprises two parts, namely anupper portion 8 a resting on a base portion 8 b. It should be noted,however, that upper portion 8 a and base portion 8 b may actually beformed as a unitary structure. Or for that matter, upper portion 8 a mayactually be an extension of cross section 4. Be that as it may, baseportion 8 b of support structure 8 has an opening 10 through whichaccess can be gained to the area of the frame underneath cross beam 4and between support structures 6 and 8. This area may simply be referredto as the work or working area. As further shown in FIGS. 1 and 2, theworking area can also be accessed from either side of cross beam 4, suchas for example via directional arrows 12 and 14. To provide exhaustventing (which will be discussed in detail later) a bore 16 is providedin support structure 6.

With respect to cross beam 4, note that it has been designed in the formof a trapezoid, with the base being wider than the top. See FIGS. 12 and13. The inventors have found that such trapezoidal design provides anefficient support of the cutting head of the present invention lasercutting system. To provide additional rigidity to frame 2, two trusssupport beams 16 and 18 fixedly couple support structures 6 and 8 attheir respective bases.

A frame for supporting a worksheet processing apparatus such as forexample a laser cutting head is shown in FIGS. 3 and 4. In particular, abase member 20 has fixedly mated thereto an arm 22 that has equalportions extending from either side of base member 20. As best shown inthe top perspective view of FIG. 4, base member 20 has bolted to itstop, which is the portion that is to be movably coupled to the undersideof cross beam 4, a number of mounts 24 that are to be coupled to thebearings of a linear guide, to be discussed laser. Also coupled to thetop of base member 24 are two sets of support members 26 and 28 to whichrespective drive motors in the form of magnetic drives manufactured forexample by the Siemens or Krauss Maffei Companies, are mounted. Themagnetic drives may also be referred to as linear drives. Two centersupport members 30 coupled to the top of base member 20 provide mountingsupport for a linear scale that measures the distance traversed by basemember 20 with reference to the longitudinal axis of cross beam 4. Moreon that later.

The underside of arm 22 is best shown in FIG. 3. As illustrated, thereare two guiding rails 32 and 34 extending substantially the entirelength of arm 22. Movably mounted to guide rails 32 and 34 is a lasercutting head support frame 36 that has a front portion, designated 38,that is configured to accept a conventional cutting head made by anumber of manufacturers including such as for example the PrecitecCompany of Germany. The movement of frame 36, and therefore the lasercutting head mounted thereto, may be effected by a linear drive motorsuch as for example the aforenoted magnetic drives or some otherequivalent motor so that cutting head support frame 36 is movablebidirectionally, per indicated by bidirectional arrows 40.

As noted with respect to the discussion of base member 20 in FIG. 4,there are two coil sliders of the linear drive motor that are coupled tosupport members 26 and 28. These coil sliders, which may be simplyreferred to as the linear motor or magnetic drives, would move betweenmagnets 40 a, 40 b and 42 a and 42 b, when base member 20 is movablycoupled to the underside of cross beam 4. See the bottom view of frame 2in FIG. 5. Further shown to be coupled to the underside of cross beam 4are linear guides 44 a and 44 b, which work cooperatively with mounts 24of base member 20.

In addition, a linear scale 46 that extends substantially along theentire length of the underside of cross beam 4 works cooperatively withthe scale mounted to support members 30 of base member 20 to provide anindication of where along the longitudinal axis of cross beam 4 the basemember is at any moment. Such linear scale is manufactured by theHeidenhain company of Germany. For our discussion, the movement of basemember 20 along the longitudinal axis of cross beam 4,is deemed to bealong the x direction. Similarly, the bidirectional movements of cuttinghead frame 36 along the longitudinal axis of arm 22 mounted to basemember 20 are deemed to be movements along the y direction. The samelinear drive that may be purchased from either the Siemens or the KraussMaffei Companies of Germany could be used for both the x and the ymovements of base member 20 along cross beam 4, and frame support 36along the length of arm 22, respectively.

FIG. 6 illustrates perspectively base member 20 being mounted to theunderside of cross beam 4 of frame 2. FIG. 7 is yet another perspectiveview of base member 20 being movably mounted to the underside of crossbeam 4 and is therefore movable along the x direction, as indicated inFIG. 6. Frame 36 to which the laser cutting head is being mountedlikewise is movable along the y direction so that by controlling therespective movements of base member 20 along cross beam 4 and framemember 36 along arm 22, the laser cutting head mounted to frame 36 canbe moved to any portion of the area underneath cross beam 4 definedbetween support structures 6 and 8.

FIG. 8 is a cross-sectional view of the frame structure 2 of the instantinvention. In addition, it shows base member 20 being disassembledlyassociated relative to the underside of cross beam 4. Frame 36 isfurther shown being disassociated from arm 22. For the purpose ofillustrating the relationship between frame 36 and the laser cuttinghead, note that laser cutting head 48 is movably mounted to the front offrame member 36, while a servomotor 50 that drives cutting head 48 alongthe direction as indicated by directional arrows 52, i.e., the z axis,is shown to be mounted to the back of frame member 36.

FIGS. 9, 10 and 11, in combination, show the three openings, once thelaser cutting system has been equipped with the appropriate covering anddoors, that could be used to gain access to the work area of the lasercutting system defined between the two support structures 6 and 8. Inparticular, as shown in each of FIGS. 9, 10 and 11, a cabinet or housing52 is provided adjacent to support structure 6. Housing 52 may be usedto contain the electrical components such as for example the CNCprocessing unit that controls the respective operations of the lasercutting system. Also provided adjacent to support structure 6 is anothercabinet or housing 54 that houses the laser beam resonator or generatorof the system. The generation of the laser beam, and its path inrelation to frame 2, will be discussed later. For the time being, itsuffices to note that FIGS. 9 and 11 show two doors 56 a and 56 b thatare adaptable to be opened so as to allow the accessing of a workpieceor worksheet 58 placed on top of a worktable, or cassette, 60 within thework area defined between support structures 6 and 8.

FIG. 10, on the other hand, illustrates the fact that the inside of thework area defined between support structures 6 and 8 may be accessedthrough opening 10 by raising a door 62. This is useful for thoseinstances where perhaps a conveyor may be provided at opening 10 toconvey worksheet 58 into and/or out of the working area of laser cuttingsystem 2. FIG. 10 moreover shows two additional doors 64 a and 64 bmovably fitted to the other side of cross beam 4 and adaptable to beopened so as to allow access to the working area of the laser cuttingsystem. Note that doors 56 a, 56 b and 64 a, 64 b may each be replacedby respective single doors 56 and 64. Also, a relatively smallermaintenance door, not shown, may be provided at either side of thesystem of the instant invention.

In sum, frame 2 of the laser cutting system is designed such that itenables the accessing of its working area from three directions, eachindependent of the other. This allows a more efficient utilization ofspace by the user, insofar as the laser cutting system may be placed atsuch a location that gaining access to the working area of the systemthat otherwise would have posed a problem by other laser cutting systemscould easily be done with the laser cutting system of the instantinvention.

Given the configuration of the frame of the instant invention, whendoors 62, 56 a, 56 b and 64 a, 64 b are closed, as per required duringthe operation of the laser system, passages that allow air to flow intothe interior of the system per paths indicated by arrows 3 and 5 areestablished. Thus, air from the environment are sucked into the interiorof the system for replacing the air that is sucked out by the vacuumcreated in the work table or cassette, the details of which will bediscussed with respect to FIGS. 28 and 29, infra.

FIGS. 12 and 13 are respective perspective views of the trapezoidalcross beam 4 and the mounting thereto at its underside of base member20, and the mounting to arm 22 of base member 20 by laser cutting head48. FIGS. 12 and 13 in essence illustrate that with the particulardesigns of cross beam 4, base member 20 and arm 22, a most efficientsystem that enables a fast positioning of cutting head 48 is achieved.This design is quite different from the conventional “gantry” typesystems whereby the laser cutting head is mounted to a cross beammounted to support members, which are movable relative to the worktable.

Further with respect to cross beam 4, insofar as it has an upside downtrapezoidal cross section, it is found that both of its sides and itsunderside are enveloped by the air that is being sucked into theinterior of the system via paths 3 and 5. Accordingly, the sucked in airprovides an air shield around the linear drives, and any coveringthereof, mounted to the underside of cross beam 4 and arm 4 to therebyprotect those linear drives or the covering to those drives from beinghit by the debris or particles that result from the fabrication of theworksheet. Additionally, the sucked in air could dislodge dirt thatmight otherwise accumulate at the drives and their covers.

FIGS. 14 and 15 illustrate the pathway in which a laser beam 66 isoutput from a laser resonator 54 to cutting head 48 and out of itsnozzle 49 for piercing a worksheet. Specifically, inside laser resonatorcabinet 54 a laser resonator 68 would generate a laser beam that isoutput from an optical output coupler 70. The laser beam is thenreflected by mirrors 72 and 74 So as to be emitted at output port 76along the direction indicated by beam path 78. A laser mirror 80 allowsthe laser beam 66 to be routed to a target 82 for alignment purposesand, at the same time, redirects the laser beam 66 along laser path 84to yet another mirror 86 that redirects the laser beam to cutting head48 and out of its nozzle 49, as shown in FIG. 14. Output coupler 70 andother beam mirrors maintain the distance of the laser beam being outputto a predetermined distance that is deemed to be useful, i.e., bymaintaining the requisite density and power for the laser beam to piercea worksheet. The laser generator inside laser cabinet 54 can bepurchased from a number of companies including for example theWegmann-Baasel Company of Germany.

An improvement to a conventional laser resonator of the instantinvention laser cutting system is the utilization of a telescopic lens88, that is controllable for example by a servomotor such as 90, whichautomatically focuses the laser beam to maintain a constant density andpower for the laser beam for a predetermined distance away from outputport 76. By maintaining a constant density and power for the laser beamfor the predetermined distance, such as for example 5 meters away, thebeam is able to perform optimal piercing and cutting of a workpiece. Asshown in FIG. 15, such predetermined distance may extend from the outputof output port 76 to substantially the full length of the area betweensupport structures 6 and 8, so as to accommodate the movement of lasercutting head 48 mounted to base member 20 along the length of cross beam4.

The telescopic lens system may comprise a telescopic lens 88 that ismovable along the length of the laser beam so as to provide a focusingeffect to maintain constant the density and power of the laser beamoutput from window 76. In place of a movable telescopic lens such as 88,a mirror type telescope system may also be used. In conjunction with theservomotor such as 90, a threaded screw or other types of drivemechanism may be used for moving telescopic lens 88 relative to outputcoupler 70. Note also that even though resonator cabinet or housing 54is shown not in contact with frame structure 2, in actuality, resonatorcabinet 54 may be physically coupled to frame structure 2, as forexample by links and bolts, so that both laser resonator 68 and framestructure 2 may be moved in unison to thereby maintain the alignment ofthe laser beam with respect to frame structure 2.

With the telescopic system, auto-focusing of the laser beam, withrespect to the worksheet, can be effected by providing a feedback signalfrom the cutting head to the CNC controller that informs the controllerwhether or not focusing is required. When the feedback received from theCNC controller indicates that indeed focusing is required, the CNCcontroller would send a signal to servomotor 90, or to be more precisevia instructions to the controller of servomotor 90, to move telescopiclens 88 relative to coupler 70 so as to automatically refocus the laserbeam, to thereby maintain constant its density and its power. Theproviding of a feedback of the cutting head to the CNC controller willbe further described with the discussion of the cutting head in FIG. 18.

Although not shown, there is provided within electronic cabinet 52, inaddition to CNC controller, at least one memory store (hard disk, tapedrive, magnetic memory store, etc.) that contains information in regardto the focal movements during fabrication of the worksheet, such as forexample piercing or cutting, so that lens 88 can be repositionedrelative to output coupler 70 each time the laser beam reaches its stoppoint. This allows the focal point of the laser beam to be adjusted evenduring the fabrication of the worksheet. Thus, the auto-focusingfunction of the laser cutting system of the instant invention has threedifferent subfunctions. These include: (1) to change the focal pointaccording to the selection of the type of worksheet material; (2) tochange the focal point on line according to the length of the laser beamof the laser cutting system; and (3) to effect focal movements duringpiercing so as to have the maximum energy at the point where actualpiercing takes place. Subfunction 2 is meant to provide compensation forthe beam divergence when the laser beam path is somewhat longer than theoptimal predetermined beam path, and subfunctions 3 is used to reducethe piercing time.

As for the types of materials that may be affected by the focal pointchanges, note that depending on the type of material to be cut, thefocal point may actually be located negatively, positively or at zero,with respect to the worksheet. This is because the focal point of thelaser beam may actually be somewhat above, below or at the surface ofthe worksheet. For example, a normal steel worksheet that has athickness of approximately 1-6 mm requires that the focal point be atthe surface of the worksheet. Alternatively, a normal steel worksheetthat has a thickness of approximately 8-20 mm requires that the focus ofthe laser beam be approximately 1 mm above the surface of the worksheet.Furthermore, a stainless steel worksheet with a thickness ofapproximately 1-10 mm requires that the focal point be negative, i.e.the focal point is below the bottom surface of the worksheet beingprocessed. As for a worksheet that is made of aluminum having athickness of 1-6 mm, the focus of the laser beam is deemed to be atoptimum at approximately {fraction (1/3 )} of the thickness of theworksheet below the surface of the worksheet. Worksheets made of othermaterials such as for example wood and other synthetics require lessstringent focal points. Of course, other parameters and known factorssuch as for example the power of the laser beam and the density of thelaser beam may also need to be taken into account to effect the positionof the focal point.

During fabrication such as for example piercing, to enable the system ofthe instant invention to continuously adjust the focal point on line, aset-up table or memory store that contains the start point and the stoppoint is provided to the CNC controller for repositioning the cuttinghead along the z direction to effect auto-focusing. For the instantinvention, this is done by taking into consideration the actual lengthof the laser beam (from the laser resonator output to the cutting headalong the x and y directions), and comparing it with the maximumpredetermined laser beam length. The maximum useable length of the laserbeam in turn is divided into a number of quadrants, or zones. Each ofthe zones is provisioned (in the set-up table or memory store) with aparticular correction factor so that when the actual laser beam lengthfalls within that quadrant, the correction factor, be it a negative orpositive number, is used to adjust the focal point of the laser beam.

For further illustration, see FIG. 31 which shows the maximumpredetermined length of the laser beam, designated as 220. The maximumlength of the laser beam in turn is divided into a number of sectors,quadrants or zones 222 a-222 h etc. A correction factor, such as forexample 0-0.5 mm in zone 222 a, is provided in each of the zones. Alsoshown in FIG. 31 is the actual length of the laser beam, designated forexample by 224 a and 224 b, representing the x and y axes of the beampath, respectively. Thus, for the exemplar laser beam 224 shown in FIG.31, given that it ends at zone 222 g, a correction factor of 3-3.5 m, beit positive or negative, is added to the focal point by refocusing thelaser beam via, for example, the movement of telescopic lens 88 relativeto output coupler 70 (as shown in FIG. 14). Note that even though thecorrection numbers in zones 222 are shown as positive numbers, inactuality, these numbers are integers that could be either positive ornegative numbers, depending on the type of materials being fabricated,so that the auto-focusing of the focal point may be effected eitherabove the worksheet, below the worksheet, or at the surface of theworksheet, as previously discussed. Thus, there may be stored in theset-up table a plurality of the exemplar series of zones as shown inFIG. 31, one for each type of material of the worksheet that is to befabricated.

Another improvement of the present invention laser cutting system is theuse of a particular type of mirror at a location such as 80 for enablinglaser beam 66 to be aligned per target 82, without having to have thecomplete mirror assembly disassembled as required by most of the priorart laser cutting systems. Specifically, as shown in FIG. 16, theimproved laser mirror 80 of the instant invention has a block portion 91that has a notch 92 a and another notch 92 b. By thus providing therespective notches, a laser beam such as 66 that is output from outputport 76 from the resonator housing can directly pass through block 91and be aligned with target 82. Thus, the only thing that needs to bedone with respect to reflective mirror 80 for the laser cutting systemof the instant invention is the removal of the actual mirror itself,such as 94 shown in FIG. 17, without having to remove the mirror block91 from the system. Contrast this with most of the prior art lasercutting systems that require the removal of the mirror blocks from thesystem in order to align the laser beam, which means that after thealignment of the laser beam, the mirror block further has to bereassembled. Oftentimes, such reassembly would cause misalignment of thelaser beam. For the instant invention, the fact that the mirror block 91is not removed means that once the laser beam is aligned, it remainsaligned as it is only mirror 94 that is removed from reflective mirrorassembly 80.

As shown in FIG. 17, mirror 94 is matably mounted to mirror block 91 andfixedly coupled thereto by means of bolts 96. As is well known, mirror94 has complemented thereto circulation tubings such as 98 that allowcooling fluid be directed to the mirror (actually behind casing 100), soas to maintain the temperature of the mirror constant as it is beingimpacted by the laser beam. By providing cooling to the mirror, themirror is prevented from warping to thereby ensure the integrity of thelaser beam.

FIG. 18 shows a conventional type of cutting head that can be purchasedfrom a number of manufacturers including for example the PrecitecCompany of Germany. As shown, cutting head 48 has a collision protectionmounting 100 that is coupled to frame member 30 for absorbing any impactcutting head 48 may have with frame member 30 when the former is drivenin a vertical direction along the z axis. A top mounting 102 provides acoupling to frame member 30 to allow a conduit through which the laserbeam may pass. An upper focusing part 104 of laser head 48 enables theuser to adjust the focus of the laser beam, per moving the focusinglens, which is held by a lens holder 106, for adjusting the focal pointof the laser beam.

The focusing of the laser beam may also be effected in a directionsubstantially perpendicular to the z direction by using a control screw108. In fact, for the laser cutting system of the instant invention, itis envisioned that the adjustment of the focusing lens being held bylens holder 106 be effected by servomotors that take into account thefeedback provided by a capacitance or non-contacting sensor 110 thatsenses the distance separating the tip of the laser cutting head fromthe top surface of the worksheet. The signal from the electrode 110 inturn is sensed and forwarded to electrode cable 112, which is shown, perdotted line 114, to be inserted into the sensor portion 116 of thecutting head. Electrode cable 112 in turn is connectable to apreamplifier 118 that in turn is electrically connected to the CNCcontroller for relaying thereto whatever signals are sensed by sensor110, to thereby establish the feedback for determining how far the tipof the cutting head is from the surface of the worksheet.

Cutting head 48 further includes an adapter portion 120 to which lowerinsert portion 116 is matable with. Adapter 120 in turn is mated withupper part 104, so as to enclose lens holder 106. Cutter head 48 furtherincludes a ceramic non-conductive tip 112 that is mated to the tip ofinsert portion 116. A nut 114 secures ceramic portion 112 to the lowerinsert 116. A nozzle electrode 118, which is fitted to ceramic portion112, completes the laser cutting head 48. It is through electrode nozzle118 that the laser beam is output for fabricating the worksheet. Forthose instances where non-metallic worksheets are being fabricated, atactile electrode or contacting sensor 120 is used in place of nozzleelectrode 118.

FIG. 19 illustrates the improvement to the cutting head shown in FIG. 18for the laser cutting system of the instant invention. In particular,prior to the instant invention, lens 122, which is held by lens holder106, in effecting the focusing of the laser beam 66, is assisted by theinput of lasing gas within the space designated 124. This is all welland good so long as the debris, particles and parts that result fromworksheet 58 being pierced or cut by laser beam 66 does not ricochetback into chamber 24 and end up impacting the lower surface of lens 122.Given that the cost of focusing lens 122 is high and its sensitivity isof relative importance, by exposing lens 122 to potential impacts causedby ricocheting debris or particles, the life expectancy of lens 122 isshortened. In fact, one of the major cost of a laser cutting system isthe often replacement of lens 122.

The laser cutting head of the instant invention overcomes thisshortcoming by interposing a partition window 126 between focusing lens122 and nozzle 118. Partition window 126 may be made of diamond or someother translucent material that has the same qualities of diamond, i.e.,hardness and resistance to scratching, and the characteristic ofallowing laser beam 66 to pass therethrough without much effect. Notethat although partition window 126 is shown to be located at the lowerpart of lower portion 120, it could in fact be placed within lowerinsert 116, which is held in place by nut 114. Given that the space fromthe tip of electrode nozzle 118 to partition window 126 is much lessthan the volume provided in chamber 124, the amount of lasing gasprovided to input 128 that acts in conjunction with laser beam 66 topierce the worksheet can be substantially reduced. Partition window 126therefore achieves the dual objectives of prolonging the life of lens122 as well as decreasing the amount of lasing gas required for coactingwith the laser beam for piercing the worksheet.

With reference to FIG. 20, the maintenance of the optimal power for thelaser beam that works hand in hand with the auto-focusing of the focalpoint is described. As is known conventionally, when output from thelaser resonator, the laser beam is never quite parallel. In other words,the laser beam tends to be slightly diverted so that it would appearsuch as the beam 66 shown in FIG. 20. That notwithstanding, as wasmentioned previously, a portion of the laser beam nonetheless is useful,provided that the diameter of that portion of the laser beam is kept tobe substantially parallel so as to contain substantially the samediameter and the same density. For laser beam 66 shown in FIG. 20,assume for the moment that such parallel portion exists at the portionof the beam designated 130. Thus, so long as focus lens 122 (cuttinghead 48 is not shown for the sake of simplicity) is moved within thedistance designated by 130, an accurate focal point is provided for aworksheet placed on worktable 60. But as it can be seen in FIG. 20,worktable 60 in fact extends beyond distance 130 whereby the density ofthe laser beam is maintained constant. What this means is that the focalpoint of the laser beam, for example 132, would be off for the portionof the laser beam that diverges. This is equivalent to the laser beamlosing power because of its distance from the laser resonator 68. Forthe instant invention laser cutting system, to compensate for this lossof power, worktable 60 is divided into a number of predetermined zonesor sections each having correction data that may be obtained empiricallyon a prototype laser cutting system that has undergone a great number oftesting.

For the exemplar system shown in FIG. 20, therefore, suppose instead ofbeing directed to an area 60 j of worktable 60 (assuming area 60 j isthe area on the worksheet placed over worktable 60 at which laser beam60 is piercing), focusing lens 122 is to be focused onto the portion ofthe worksheet that superposes over section 60 k. At this point, notethat laser beam 66 has substantially diverged. From the empirical datacollected and stored in the memory store which is retrievable by the CNCcontroller, suppose that at area 60 k of worktable 60, there is provideda correction data of 0.10 mm. Given that and the fact that the CNCcontroller gets a feedback from the capacitance sensor 110 (FIG. 18) ofthe distance separating the cutting head from the surface of theworksheet, appropriate correctional movement may be output by the CNCcontroller to instruct the servomotor to reposition focusing lens 122with the appropriate correction data which, in this instance, is 0.10 mmtoward the worksheet (assuming that the correction is plus 1.0 mm inthis instance). Therefore, by dividing the worktable into differentzones, areas or sections having their respective coordinates in terms ofthe x and y axes, the worktable in essence is divided into a number ofmatrixes each having its own correction data that can be used to correctany divergence of the laser beam, to therefore maintain a laser beamthat has substantially the same power density for every area on theworktable onto which a worksheet may be placed.

FIG. 21 illustrates in a simplified schematic format the controlling ofthe adjustment of the laser beam by the CNC controller. This correspondsto the laser resonator portion shown in FIG. 15 in which the beam widthand density of laser beam 66 can be controlled by the interactionbetween output coupler 70 and telescopic lens 88, which is driven by aservomotor 90. The instructions for activating servomotor 90 for drivingtelescopic lens 88 in relation to output coupler 70 are provided by theCNC controller, which in turn receives feedback from cutting head 48.

The way in which the cutting head is moved relative to a worksheet forthe instant invention laser cutting system is effected by a “ping pong”process whereby an optimal movement of the cutting head is calculatedfor moving it from one location to a next location on the worksheet. Inparticular, with reference to FIGS. 22 and 23, note that a worksheet mayhave already cut thereinto a number of holes or cuts. The ping pongprocess of the instant invention allows the laser cutting headpositioned at a first location, for example at 130, to be moved to anext location, for example 132, at an optimal rate. This is done by theCNC controller, in conjunction with an interpolation process, based onthe determination of a number of things.

One of the items that is determined is the focal distance that separatesthe nozzle from worksheet 58, for example the distance designated 134.Another item that needs to be determined is the distance separating thelocation where the cutting head is and the next location where thecutting head needs to be for the next fabrication process on worksheet58. In other words, the CNC controller has to know the distanceseparating points 130 and 132. For the interpretation process, it isassumed that the shorter the distance between 130 and 132, the lesslikely the cutting head needs to be elevated along the z direction asindicated in FIG. 22. On the other hand, if the distance separatingpoints 130 and 132 is great, and if cutting head 48 were to be elevatedsufficiently above worksheet 58, the speed at which cutting head 48 maybe moved between the two locations can be incrementally increased. Suchelevation of cutting head 48 is indicated in FIG. 22 by, for example,dotted lines 136 and 138. Note that 138 indicates that cutting head 48is to be moved further away from worksheet 58 inasmuch as the nextlocation to which it is to be moved is further than location 132. Ofcourse, it is understood that the higher cutting head 48 is elevatedfrom worksheet 58, the less the chance that any flexing of worksheet 58could cause it to come into contact with cutting head 48.

For those instances where the worksheet already has prefabricated holes,either through previous punching or cutting, when laser head 48encounters such a hole, such as for example 140 shown in FIG. 22, due tothe capacitance sensing of the distance separating the surface ofworksheet 58 and the nozzle electrode of cutting head, prior to theinstant invention ping pong process, the cutting head would naturallymove down towards worksheet 58 since it has no knowledge that hole 140is present; and in certain instances, if a predetermined stop distancehas not been programmed into the CNC controller, cutting head 48 wouldactually come into contact with worksheet 58. The movement process ofthe instant invention eliminates such inadvertent contact by instructingcutting head 48 to move from a first location to a next location by anelevation vector such as 139, distance permitting between the locations.In other words, cutting head 48 would, similar to the actions of a pingpong ball, bounce from one location to the next.

To obtain the optimal movement for cutting head 48, a number ofparameters are programmed into the CNC controller so that the variousoperations for fabricating a hole or cut in a worksheet aresynchronized. To wit, the movement of the laser cutting head 48 issynchronized with the outputting of the laser beam from the laserresonator. For example, when the laser cutting head has finishedpiercing a hole in a first location, just before cutting head 48 is tobegin its movement to the next location, the laser beam is turned off atthe laser resonator. And just prior to cutting head 48 reaching the nextlocation, for example 132, the laser resonator would begin to generatethe laser beam so that the output of the laser beam is timed such thatit begins to pierce worksheet 58 as soon as cutting head 48 has stoppedat location 132 and the focal point separating cutting head 48 andworksheet 58 is at the appropriate height. The same process is effectedwith the respect to the movement of cutting head 48 to its nextlocation. For example, as soon as the piercing or cutting of worksheet58 is completed at location 132, cutting head 48 begins its movement tothe next location at the predetermined elevation and speed, and thelaser resonator begins to turn off the laser beam. This process isrepeated until all locations on the worksheet that need to be fabricatedare done.

FIG. 23 provides an illustration of the relationship between thedistance separating different locations and the speed with which cuttinghead 48 is moved. For example, the distance separating locations 142 to144, as represented by the shown circles or holes, is greater than thedistance separating locations 144 and 146. Accordingly, cutting head 48may be elevated to a higher height and moves faster from location 142 to144. Insofar as location 144 to 146 is separated by a shorter distance,the elevation of cutting head 48, if any, would be lower than theelevation of cutting head 48 between locations 142 and 144, as ittravels from location 144 to 146. An optimal time nonetheless ismaintained for cutting head 48 to move from location 144 to location 146insofar as the distance separating those locations is relatively short.Putting it simply, there is no need to elevate cutting head 48 if thedistance separating a first location to a second location is small, forexample 5 mm. Thus, by determining the coordinates in which lasercutting head has to move and the spatial relationship between thevarious locations, an optimal movement for moving cutting head 48 fromlocation to location superposing the worksheet can be interpolated.

A flow chart illustrating the process of moving the laser head of theinstant invention is given in FIG. 24. The process begins by determiningthe focal distance between the laser cutting heard and the worksheet atstep 150. At or about the same time, a determination is made of thedistance separating the various locations per step 152. Further, adetermination is made on the distance separating the nozzle from theworksheet per step 154. These determined data are taken intoconsideration with various predetermined parameters which, in additionto those mentioned previously, may also include the weight of the lasercutting head, the acceleration and deceleration that are needed formoving the laser head and stopping it, and other data such as forexample how long it takes the laser beam to be turned on and off andtravel to the cutting head, etc. Using these various parameters anddetermined data, the optimal movement for the laser cutting head isinterpolated per step 156. Thereafter, the instructions to the cuttinghead for the optimal movement are generated per step 158. With thoseinstructions, the CNC controller can instruct the motor mechanism suchas for example the linear drives and the servomotors to move the lasercutting head from one location to the next, per step 160. The laser beamis generated and provided to the cutting head per step 162 right beforethe cutting head gets to its next lactation. Thereafter, the output ofthe laser beam is synchronized with the movement of the laser cuttinghead so that the laser beam is output as soon as the movement of thecutting head has stopped, per step 164. Step 164 takes into account thetermination of the laser beam as the laser cutting head begins itsmovement to the next location. At step 166, a determination is made ofthe next location to which the cutting head is to be moved. And adetermination is made per step 168 on whether all cuts have beeneffected on the worksheet. If no, the process continues. If all cutsindeed have been made on the worksheet, the process stops.

With reference to FIG. 25, worktable 60 that is placed in the workingarea of the laser cutting system of the instant invention is shown.Worktable 60 may also be referred to as a cassette. As shown, worktable60 has a frame 170 that comprises two long sides 172 a and 172 b, andtwo short sides 174 a and 174 b. Frame 170 is movably mounted on tworails, or slides, 176 and 178. Insofar as worktable or cassette 60 ismovable along the y direction, the worksheets placed thereon (eitherbefore fabrication or afterwards), can be retrieved readily from eitherside of the laser cutting system, as shown for example in FIGS. 10 and11, as frame 170 can be readily moved through doors 56 and door 64 atrespective sides of the laser cutting system of the instant invention.As best seen in FIG. 27, frame side 174 b rolls per roller 180 alongrail 178 while frame side 174 b slides along rail 178.

Further with reference to FIG. 25, it can be seen that there are anumber of support brackets 182 extending along the x direction of frame170. With specific reference to FIGS. 26 and 27, a plurality of strips184 each extending along the y direction of frame 170 from side 172 a to172 b are shown. These strips are supported by base members 186, only afew of which are shown in frame 170 in FIGS. 26 and 27. Formed along thelength of each of strip members 184 are a corresponding number of bores188 into which a number of pins 190 are fixedly mated to. Each of pins190 has a replaceable tip that is made of a soft metal such as forexample copper or brass. Further mounted to frame 170 is a plurality ofribs 194. These ribs are mounted to selected slots 196 of the supportbrackets along the length of frame 170 at the x direction, and areinterspersed with the plurality of strips having the bores through whichpins 190 are mounted. Each of ribs 194 has an upper or top portion thatis shaped with a number of contiguous teeth 198.

Thus, frame 170 has alternate rows of pins and teeth along its xdirection for supporting a worksheet, such as for example 58 placedthereon. In fact, tips 192 of pins 190 form a plane that is slightlyhigher than the plane that is formed by the tips of the various teeth198 of ribs 194. The fact that the pins form a higher support plane thanthe teeth means that the worksheet is mainly supported by the pins. Thisis desirable insofar as there is less of an area of the worksheet thatis being supported. The fact that tips 192 of pins 190 are replaceablemeans that when the tip of a pin is worn out, such as for example bybeing repeatedly impacted by the laser beam, only that tip needs to bereplaced, as there is no need to replace the entire pin. The ribs areused to support those portions of the worksheet that are either cut fromthe worksheet or have sagged somewhat.

FIGS. 28 and 29 are respective perspective views of the base onto whichworktable or cassette 60 is mounted. Base 200 is made of a platform 202that is divided into a number of sections 204 a-204 f. Platform 202 inturn is mounted to two tubular chutes 206 and 208 by means of legs 210.Chutes 206 are hollow ventilation chutes that has a number of openings212 formed therealong which are adaptable for receiving a tube 214 thatconnects the opening to an opening of a corresponding one of sections204 a-204 f. Tubes 214, only one of which is shown for the sake ofsimplicity, is movable vertically by means of a corresponding hydrauliccylinder 216 for connection to its corresponding section. By providingvacuum in chute support 206, a vacuum is created at the appropriatesections 204 so as to suction the dust particles and/or exhaust gases orfluids that result from the piercing or cutting of the worksheet by thelaser beam. The dust particles thus suctioned are collected and ventedthrough chute output 218, which in turn is connected to vent 16 (FIGS. 1and 2), so that the fall out dust particles are collected and removedfrom the work area of the laser cutting system. By synchronizing thecutting of the worksheet, the location of the worksheet where the cut isbeing effected, and the section of base 200 activated for suctioning,most, if not all, of the dust particles and waste gases from the laserbeam cutting of the worksheet are removed.

FIG. 30 is a cross-sectional view of the laser cutting system of theinstant invention. In essence, it shows the relative positioning of thevarious components of the system by overlaying the frame structure withthe worktable and the base to which the worktable is movably superposed.

Inasmuch as the present invention is subject to many variations,modifications and changes in detail, it is intended that all mattersdescribed throughout this specification and shown in the accompanyingdrawings be interpreted as illustrative only and not in a limitingsense. For example, even though the work processing apparatus describedhereinabove relates to a laser cutter, it should be appreciated thatother work processing apparatus such as for example a punch or a cuttermay also utilize the frame structure of the present invention.Accordingly, it is intended that the invention be limited only by thespirit and scope of the hereto appended claims.

What is claimed is:
 1. A work table comprising: a frame; a plurality ofribs superposed over said frame; a plurality of strips, except for endpieces of said strips, each mounted between an adjacent pair of saidribs, said strips each having a number of bores formed therealong; and aplurality of pins each fitted to a corresponding one of said bores forforming rows of pins interspersed with rows of ribs for supporting aworksheet placed thereon.
 2. Work table of claim 1, further comprising:a plurality of bracket means extending along at least one direction ofsaid frame for supporting said plurality of ribs.
 3. Work table of claim1, wherein said ribs each are made of a strip of metal having a baseportion and a top portion shaped with a number of contiguous teeth, saidteeth having respective tips being positioned at a slightly lower planethan that of the tips of said pins for supporting said worksheet. 4.Work table of claim 2, wherein each of said bracket means comprises alongitudinal member having equally spaced slots formed therealong, atleast every other one of said slots for said each member being used foraccepting a corresponding one of said ribs so that said plurality ofribs each are fitted at equidistance from its adjacent ribs withcorresponding rows of pins, except for two end ribs, separating saidadjacent ribs.
 5. Work table of claim 1, further comprising: two tracksonto which said frame is movably mounted, said frame being supported byand movable bidirectionally along said tracks so as to be movable indirections that are perpendicular to the direction in which said ribsare mounted to bracket means extending along said frame.
 6. Work tableof claim 1, wherein said pins each have a top that is replaceable.
 7. Awork table to be used with an apparatus for outputting a laser beam tofabricate a worksheet, comprising: a frame positioned under saidapparatus; a plurality of ribs superposed over said frame; a pluralityof strips, except for end pieces of said strips, each mounted between anadjacent pair of said ribs, said strips each having a number of boresformed therealong; and a plurality of pins each fitted to acorresponding one of said bores for forming rows of pins interspersedwith rows of ribs for supporting said worksheet.
 8. Work table of claim7, further comprising: a plurality of bracket means extending along onedirection of said frame for supporting said plurality of ribs.
 9. Worktable of claim 7, wherein said ribs each are made of a strip of metalhaving a base portion and a top portion shaped with a number ofcontiguous teeth, said teeth having respective tips being positioned ata slightly lower plane than that of the tips of said, pins forsupporting said worksheet so as to prevent materials resulting from saidworksheet being cut by said laser beam from back splattering.
 10. Worktable of claim 8, wherein each of said bracket means comprises alongitudinal member having equally spaced slots formed therealong, atleast every other one of said slots for said each member being used foraccepting a corresponding one of said ribs so that said plurality ofribs each are fitted at equidistance from its adjacent ribs withcorresponding rows of pins, except for two end ribs, separating saidadjacent ribs.
 11. Work table of claim 7, further comprising: two tracksonto which said frame is movably mounted, said frame being supported byand movable bidirectionally along said tracks so as to be movable indirections that are perpendicular to the direction of said apparatus.12. Work table of claim 7, wherein said pins each have a top that isreplaceable.